A conventional air conditioning machine is disclosed in JP 2002-228281 A (PTL 1). The air conditioning machine includes a refrigerant circuit in which a compressor, a four-way switching valve, an outdoor heat exchanger, an on-off valve, and an indoor heat exchanger are circularly connected and a gas detector which detects leakage of a refrigerant. Once the gas sensor senses the leakage of the refrigerant, a pump down operation is carried out.
When the pump down operation is carried out, the compressor is operated with the four-way switching valve switched into a cooling operation side and with the on-off valve closed. Thus the refrigerant can be collected into the outdoor heat exchanger.